This invention relates to internal combustion engine apparatus having no speed governor, and more particularly it is concerned with an internal combustion engine apparatus suitable for use with a chain saw, a mowing machine, a sprayer, etc., of a portable type.
In one type of engine apparatus known in the art, a centrifugal clutch is combined with an internal combustion engine having an ignition system adapted to operate with a substantially constant ignition timing in all the ranges of engine speed. Meanwhile, there has been a demand for an internal combustion engine apparatus in which a centrifugal clutch is combined with an internal combustion engine having an ignition system capable of being in delayed ignition timing in a low engine speed range, being in advanced ignition timing in a high engine speed range and changing ignition timing stepwise in an intermediate engine speed range, so as to improve engine performance and operation efficiency.
However, this demand has not been met yet. The problems that have to be obviated to enable the desired internal combustion engine apparatus to be provided are as follows. In the low engine speed range in which ignition timing is delayed, the output power of the engine is low. If an attempt is made to engage the clutch while the engine is in this condition, then the engine stalls before the clutch is fully engaged, thereby preventing a further rise in engine speed. Even if the engine stall is avoided, it is inevitable that acceleration rate in the rpm of the engine speed is lessened.